Wednesday, August 26, 2009

AIS/VHF Antenna Splitter Warning

We were early adopters of Class-B AIS transponders. It seemed far better to be seen than to just see other ships. The technology has been invaluable, especially since we do not have radar.

In San Diego and back home in Berkeley, I have been watching the boat on web reporting pages (, It has only shown up sporadically on the displays. I have never quite been sure if this was due to the base station placement, some sort of Class B filtering or a problem with our transmitter.

I recently contacted True Heading AB, the Swedish company that markets our AIS-CTRX transceiver in Europe. They told me that the problem is probably due to an antenna splitter that sometimes does not forward transmissions from the AIS Class B unit.

I bought the SmartRadio splitter from a Miltech Marine. The unit looked identical to one being sold in Europe by True Heading and others. The fact of the matter is that, most all of the equipment is built somewhere in Asia and marketed under different brand names around the world.

Many vendors are now offering a new product especially for Class B that will transmit all of the time. The older model works fine for Class C receivers and has given us great VHF transmission and reception. We can commonly see ships 17 to 20 miles away with out mast head antenna.

If you have a Class B system, I would suggest checking the components in your installation.

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